The invention relates to a method and a device for regulating individual sub-flows of a system for conveying fluid media in accordance with the introductory portion of claims 1 and 7.
In systems for conveying fluid media with several parallel conveying lines, the generation of pressure is responsible for the transport of the medium. Frequently, it is necessary that the individual sub-flows, arriving at the respective conveying destination, are of the same or of a known magnitude. In such a case, it must be possible to adjust the deviating flow resistances.
The possibility of temporally coordinating the volumes (or masses), arriving at the conveying destination, is particularly important if the composition of the fluid medium is selectively inhomogeneous or if the fluid medium is a carrier for substances, which are to be transported discontinuously. Even if, during the conveying of liquid media, exact quantitative doses or also analytical determinations of a possibly changing composition in the individual conveying lines of a conveying system are required, unforeseeable flow rate times can create problems. For example, in the area of the food industry, of medical technology and also of the pharmaceutical industry, it is frequently necessary to supply certain volumes simultaneously to a particular conveying destination. In practice, different and, in some cases also, temporally changing flow resistances in the individual conveying lines stand in the way of this necessity. These different flow resistances arise due to different frictional losses in the line system and result, for example, from material defects, different flow cross sections or also blockages. For example, in the area of the food industry, of medical technology and also of the pharmaceutical industry, it is frequently necessary to supply certain volumes simultaneously to a particular conveying destination. In practice, different and, in some cases also, temporally changing flow resistances in the individual conveying lines stand in the way of this necessity. These different flow resistances arise due to different frictional losses in the line system and result, for example, from material defects, different flow cross sections or also blockages.
Until now, only the control of the pressure in the individual conveying lines was known. An example of this is shown in the U.S. Pat. No. 2,676,603. The apparatus, shown there, works with several restricting capillaries, which are brought to the same pressure level at the outlet side. The volume flows emitted are the same only at identical pressures in the discharging chambers described there, at identical pre-pressure, at identical temperature and with identical restricting capillaries. The control namely functions only if the respective counter-pressures of the units, which are to be supplied (in the case shown there of an internal combustion engine, the pressure drop at the fuel pipelines plus the drop in the intake manifold when the inlet valve is opened), are small in comparison to the regulator dwell pressure. If these counter pressures exceed a certain limiting value, the control is made inoperative and the volume flows adjust corresponding to the respective counter-pressure. In addition, the control does not notice if one of the restricting capillaries has an increased flow resistance, for example, because of a blockage. In the blocked restricting capillary, there is then a correspondingly smaller volume flow, while the pressure drop is the same.
It is an object of the invention to provide a method and a device, with which it is possible to regulate the sub-flows of the individual conveying lines of a conveying system for fluid media, as required, with only a single constant conveying unit.
This objective is accomplished with the characterizing distinguishing features of claims 1 and 7.
Advantageous further developments are given in the dependent claims.
An essential distinguishing feature of the method described here is the determination of partial flow resistances from the ratio of a total pressure P, measured before the distribution, and a sub-flow value S,, determined in each conveying line. The latter could not be attained without including the total pressure and the direct control on the sub-flow at constant total flow.
For the selection of the total pressure sensor, which determines the pressure P ahead of the distribution over the individual conveying lines, the permissible range of the total flow, as well as the possible changes in the viscosity of the conveying medium are of decisive importance. The selection of an advantageous measurement principle for determining the sub-flow value Sn depends on the particular application.
Different methods are known for measuring volume and mass flows. Criteria for the selection of flow-through measuring devices are set down in DIN 2644.
The advantages of the invention lie in the possibility of producing with the method and the device identical or selectively different sub-flows for fluid media in the conveying lines in a conveying system using a single conveying unit (such as a pump).
Each of the control devices, working strandwise, can undertake the approach of the actual value to the specified value without interference from the control processes in the other conveying lines. In contrast to this, with direct regulation of the sub-flows using a flow meter and a control valve, interference by the control processes in the other conveying lines would be unavoidable. Overall, because a constant flow is supplied, it would not be possible to control the sub-flow.
For the methods described, the conveying output and conveying pressure can be varied without disturbing the controlled equilibrium. For applications with a viscosity that varies, the specified value can be adjusted independently of the viscosity by a suitable selection and a suitable installation of the sub-flow unit.
A further, important advantage of the invention consists of determining changes in the flow resistance of individual conveying lines, which occur suddenly or slowly during the operation, for example, due to blockages during the transport of dispersions or in the case of leaks in a conveying line. If a permitted control value range is set for the valve used, the above-mentioned disturbances can be noted in good time and the conveying lines in question switched out.